Colorado River Basin

views updated May 08 2018

Colorado River Basin

Located in the southwestern United States and northwestern Mexico, the Colorado River is a 2,330-kilometer (1,450-mile) river with its headwaters in the Rocky Mountain National Park in north-central Colorado. The river is the primary source of water for a region that receives little annual rainfall.

More than 1,000 years ago, Native Americans irrigated their crops with the waters from the river. Today, the Colorado River is still used for irrigation , but it is also used to generate hydroelectric power and to supply water to distant urban areas.

The Basin

The Colorado River system, including the Colorado River, its tributaries , and the lands that these waters drain, is called the Colorado River basin, or watershed. It drains an area of 637,000 square kilometers (246,000 square miles), including parts of seven western U.S. states (Wyoming, Colorado, Utah, New Mexico, Nevada, Arizona, California) and Mexico. Three-fourths of the Colorado basin is federal land comprised of national forests, national parks, and Indian reservations. The drainage basin's total runoff is about 700 cubic meters (24,700 cubic feet) per second. It is the international boundary for 27 kilometers (17 miles) between Arizona and Mexico.

Water Resources.

The Colorado River Basin offers a major renewable water supply in the southwestern United States. About two-thirds of the water flowing in the Colorado River and its tributaries is used for irrigation, and the other one-third supplies urban areas, evaporates into the atmosphere, or provides water to riparian (streamside) vegetation. Without Colorado River water, the region would support few crops, and major cities such as Las Vegas, Nevada, and Phoenix, Arizona, would not have grown so rapidly.

Today nearly 17 million people depend on the Colorado's waters. The basin population has expanded dramatically in recent years, with most growth occurring in urban areas, where about 80 percent of the region's residents live. Phoenix and Tucson, Arizona, and Las Vegas, Nevada are the largest cities in the basin, and they use the Colorado River and its tributaries as their primary source of water.

Water from the Colorado River is taken from its primary route and transported to locations far from the Colorado River Basin. For example, water is diverted eastward across the Rocky Mountains to Denver and other cities in Colorado. The Colorado River Aqueduct carries water to metropolitan Los Angeles, and the Central Arizona Project supplies the Phoenix and Tucson areas. The All-American Canal provides water for the Imperial Valley of southern California, a productive agricultural region converted from a desert.

Multipurpose Dams.

Numerous dams were built on the Colorado and its tributaries during the twentieth century. The purpose of these dams was primarily to generate electricity, control floods, and provide recreational opportunities. They also store water during wet times for use during the dry months and, in some cases, during dry years.

The basin dams are able to store more than 86 billion cubic meters (3,037 billion cubic feet) of water, which is about four times the Colorado River's average annual runoff. The largest of these facilities, completed in 1936, is Hoover Dam, located on the border between Nevada and Arizona. The second largest dam is Glen Canyon Dam, which is in north-central Arizona and began operating in 1964. These two dams provide about 80 percent of the water-storage capacity in the basin.

The Morelos Diversion Dam, located on the MexicoArizona border, is the southernmost dam on the Colorado River. It sends nearly all of the remaining water to irrigation canals in the Mexicali Valley and to the Mexican towns of Mexicali and Tijuana. As a result, the river rarely reaches the Gulf of California, normally the river's mouth. Consequently, the vast wetlands at the mouth of the Colorado River have been reduced to just a fraction of their former size, affecting vegetation and wildlife. Before the construction of a number of dams along its reach, the Colorado flowed 129 kilometers (80 miles) through Mexico to the Gulf of California.

Hydroelectric generation from water stored at dam sites along the Colorado River totals about 12 billion kilowatt-hours per year, which is roughly equivalent to one-sixth of the electricity consumed in Arizona each year. This power is shared among several western states.

The dams of the Colorado River are used to control flooding and to permit development of flood-prone land along lower reaches. In addition, some of the reservoirs created by dams have been formed into national recreational areas comprising spectacular engineered wonders amidst natural landscapes. For example, Lake Mead National Recreation Area is made up of Lake Mead, formed by Hoover Dam, and Lake Mohave, formed by Davis Dam, while the Glen Canyon National Recreation Area includes Lake Powell.

Management Efforts

The Colorado Basin states were anxious about their shares of the Colorado River as early as the 1900s. Then as now, growth within the state of California was viewed with concern, as burgeoning expansion meant increased water demands. The signing of the Colorado River Compact in 1922 was an important milestone in the management of the Colorado River and became the foundation for the law of the river. This compact included the seven Colorado River Basin states, and apportioned water from the Colorado River between the Upper and Lower Basin states. The parties to the Colorado River compact were not unduly concerned with Indian water rights, nor did the Compact include provisions to protect the environment.

In 1963, a U.S. Supreme Court decision stated the amount of water to be apportioned among the lower-basin states, as well as the amounts that had been historically reserved for Indian tribes and federal public lands. Because of this landmark case, tribes are now considered to have the best water rights along the Lower Colorado River. The competition for water in the Colorado River Basin continues to be severe, as is shown by the increasing numbers of lawsuits that are within the court system. Water projects must now thoroughly research various environmental-impact studies in accordance with federal environmental protection legislation.

The apportionment of the waters of Colorado River has been cause for a great deal of controversy. The impact of dams and canals along the Colorado has spawned widespread debate on river development and the ecological role of instream flows. Given projected growth in its region, these controversies and debates will continue for some time.


A water quality problem that has grown in importance within the Colorado River is salinity, or the amount of solids (mostly salt) in the water. A variety of sources bring such dissolved salts into the river. The majority of salts run naturally off of soils and rocks. When river water is used for irrigation, some salts evaporate, and become concentrated in the remaining water that returns to the river. The salt problem is also caused by evaporation from reservoir surfaces and water use by plants along the river. The concentration of salt in the water of the lower river valley is so high that it cannot be used for human consumption without treatment. As a result, a desalinization plant near the border with Mexico removes salt from the river and allows the United States to provide Mexico with usable water.

Significant water quality problems occur in the Colorado River Basin, primarily because the river carries an estimated 9 million tons of salts annually. This amount is expected to increase in the future because of increased human use. Even worse, the lower Colorado River contains about 2,000 pounds of salts per acre-foot. Salinity increases downstream primarily owing to agriculture, evaporation, and the leaching of salts from soils. High salinity levels also originate in several tributaries, especially the Virgin River that flows through Arizona into Nevada. Environmental groups study the high salinity in the Colorado River and regularly meet to address this issue and other related water quality problems.

see also Dams; Desalinization; Hoover Dam; Instream Water Issues; Planning and Management, Water Resources; Powell, John Wesley; Prior Appropriation; Reservoirs, Multipurpose; Rights, Public Water; River Basin Planning; Supply Development.

William Arthur Atkins


Graf, William L. The Colorado River: Instability and Basin Management. Washington D.C.: Association of American Geographers, 1985.

Waters, Frank. The Colorado. New York: Rinehart, 1946.

Internet Resources

Colorado River Basin Salinity Control Program. Bureau of Reclamation, U.S. Department of the Interior. <>.

Colorado River Water Dispute (COLORADO Case). American University, Washington, D.C. <>.

Gillon, Kara (Defenders of Wildlife). The Lower Colorado River Basin: Challenges of Transboundary Ecosystem Management. Border Information and Outreach Service (BIOS), Interhemispheric Resource Center (IRC). <>.

The Colorado River: Lifeline of the Southwest., Digital West Media, Inc. <>.

Colorado River Explorations

views updated May 11 2018


COLORADO RIVER EXPLORATIONS. The Spanish explorer Francisco de Ulloa unwittingly reached the mouth of the Colorado River, in the Gulf of California, in 1539, but it was not until the following year that Hernando de Alarcón braved the fierce tidal bore of the river's mouth and proceeded upstream in boats drawn by tow ropes. Though Alarcón did not meet with Francisco Vásquez de Coronado's overland expedition, two of Coronado's officers, Melchior Díaz and García Lopéz de Cárdenas, did reach the Colorado that same year. Indeed, Cárdenas is generally credited as being the first European to see the Grand Canyon.

The Colorado River was given its name by Franciscan missionaries, who were the predominant explorers of the next two centuries. The name came from the river's red tinge during the spring melt. While missionaries traveled the Colorado frequently during this period, their missions were more concerned with converting souls than they were in contributing to the geographical knowledge of the region. One exception among the Franciscans was Silvestre Vélez de Escalante, who explored the river in the 1770s.

American trappers and fur traders were the next group of Europeans to take interest in the Colorado. William H. Ashley organized the American fur trade in the Rocky Mountains and hired Jedidiah Smith, who discovered the beaver-rich Green River. Ashley himself descended the Green River—conducting the first navigation of the river—in 1825 in bullboats and provided the first authentic information regarding the upper Colorado, painting "Ashley, 1825" on a huge rock at Ashley Falls.

Whereas the early Spanish adventurers had explored the Colorado from its mouth and headed northward, the American trappers had explored the river's northern tributaries, discovering and charting the geographies of the Green River and its junction with the Colorado. The greatest explorer of the Colorado connected the two ends of the river in exploring the last unmapped part of the continental United States. John Wesley Powell, the intrepid, one-armed leader of the Colorado River Exploring Expedition, embarked on his first—and historically more significant—trip through the Grand Canyon in 1869, departing from up the Green River in western Wyoming in May. After a dangerous 900-mile journey, in which three men deserted, the party concluded its voyage at the mouth of the Virgin River, in southeastern Nevada on 29 August. Powell's subsequent expeditions were scientifically more productive than the first, and enriched by the participation of the scientific artist of such eminent geologists as Grove Karl Gilbert and Clarence Dutton as well as the archaeologist William H. Holmes. Their collaboration was instrumental in the formulation of the basic principles of structural geology. As well as the geography and geology of the Colorado River, Powell was also intensely interested in the ethnology of the region and devoted considerable time to this study. As a result of the success of the second expedition, Powell was appointed director of the Survey of the Rocky Mountain Region in 1877. In 1881 he was made bureau chief of the new U.S. Geological Survey, a position he held until 1894. The Exploration of the Colorado River of the West (1875) and The Geology of the Eastern Portion of the Uinta Mountains (1876) are among Powell's important publications from his Colorado River explorations.

While Powell might have closed the book on discovery-oriented explorations of the Colorado, the river has been explored extensively throughout the twentieth century. The damming of Glen Canyon in the 1950s required considerable analysis of sites, while recent talk of dam removal has also prompted further investigation of the river's ecology.


Pyne, Stephen J. How the Canyon Became Grand: A Short History. New York: Viking Press, 1998.

Stegner, Wallace. Beyond the Hundredth Meridian: John Wesley Powell and the Second Opening of the West. Lincoln: University of Nebraska Press, 1982.

Worster, Donald. A River Running West: The Life of John Wesley Powell. Oxford: Oxford University Press, 2001.


See alsoExplorations and Expeditions: U.S. ; Fur Trade and Trapping .

Colorado River

views updated May 08 2018

Colorado River

One of the major rivers of the western United States, the Colorado River flows for some 1,500 mi (2,415 km) from Colorado to northwestern Mexico. Dropping over 2 mi (3.2 km) in elevation over its course, the Colorado emptied into the Gulf of California until human management reduced its water flow. Over millions of years the swift waters of the Colorado have carved some of the world's deepest and most impressive gorges, including the Grand Canyon.

The Colorado River basin supports an unusual ecosystem . Isolated from other drainage systems, the Colorado has produced a unique assemblage of fishes. Of the 32 species of native fishes found in the Colorado drainage, 2166%, are endemic speciesspecies that arose in the area and are found nowhere else.

Major projects carried out since the 1920s have profoundly altered the Colorado. When seven western states signed the Colorado River Compact in 1922, the Colorado became the first basin in which "multiple use" of water was initiated. Today the river is used to provide hydroelectric power, irrigation , drinking water, and recreation ; over 20 dams have been erected along its length. The river, in fact, no longer drains into the Gulf of Coloradoit simply disappears near the Mexican towns of Tijuana and Mexicali. Hundreds of square miles of land have been submerged by the formation of reservoirs, and the temperature and clarity of the river's water have been profoundly changed by the action of the dams.

Alteration of the Colorado's habitat has threatened many of its fragile fishes, and a number are now listed as endangered species . The Colorado squawfish serves as an example of how river development can affect native wildlife . With the reservoirs formed by the impoundments on the Colorado River also came the introduction of game fishes in the 1940s. One particular species, the Channel catfish, became a prey item for the native squawfish, and many squawfish were found dead, having suffocated due to catfish lodged in their throats with their spines stiffly locked in place. Other portions of the squawfish population have succumbed to diseases introduced by these non-native fishes.

Major projects along the Colorado include the Hoover Dam and its reservoir , Lake Mead, as well as the controversial Glen Canyon Dam at the Arizona-Utah border, which has a reservoir extending into Utah for over 100 mi (161 km).

[Eugene C. Beckham and Jeffrey Muhr ]



Fradkin, P. L. A River No More: The Colorado River and the West. New York: Knopf, 1981.

Richardson, J. The Colorado: A River At Risk. Englewood, CO: Westcliffe Publishers, 1992.

Colorado River

views updated May 21 2018

Colorado River

The Colorado River is in the south of Argentina, marking the border between the provinces of Mendoza and Neuquén, La Pampa, and Río Negro. With a length of 684 miles, the river is commonly considered the northern border of the Patagonian region of Argentina. The Colorado River begins in the Andes mountain range in the province of Mendoza, at the confluence of the Barrancas River and the Grande River (its principal tributary). It flows into the Argentine Sea (Mar Argentino) in the Atlantic Ocean, to the south of the province of Buenos Aires. Its average volume of flow is more than 4,900 cubic feet per second.

The river basin can be divided into two sectors: the upper, made up of the Grande and Barrancas rivers all the way to Buta Ranquil, and the middle and lower, from Buta Ranquil to the Atlantic Ocean. The river runs in an east-southeasterly direction through a sparsely populated region. Its waters are used for irrigation, although the river could also be transformed in the future into a key waterway for shallow draft vessels.

See alsoArgentina, Geography; Mendoza; Neuquén; Patagonia.


Schard, Wernher. Los ríos mas australes de la tierra. Buenos Aires: Marymar Ediciones, 1983.

                                            Richard Reed

Colorado River

views updated May 17 2018

Colorado River Major waterway in sw USA, which rises in the Rocky Mountains of n Colorado, and flows generally sw into the Gulf of California, passing through the Grand Canyon. There are many national parks, irrigation and hydroelectric power schemes along the river. Length: 2333km (1450mi).

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Colorado River (North America)

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Colorado River (North America)